apphandler: Fix buffer underflow in ipmi_app_get_device_guid
apphandler: Fix buffer underflow in ipmi_app_get_device_guid

Change-Id: I7e27130bbe8bfc847f81968d850abacb8914ad78
Signed-off-by: Emily Shaffer <a6e326c88a51217312e91af047fa468d2d7dea8f@google.com>

openbmc/phosphor-host-ipmid,openbmc/phosphor-host-ipmid,openbmc/phosphor-host-ipmid